Repetitive myocardial stunning in pigs is associated with an increased formation of reactive nitrogen species

The “oxyradical hypothesis” of myocardial stunning proposes that superoxide, released on reperfusion, leads to contractile dysfunction via the production of the more reactive hydroxyl free radical from the iron catalysed Haber-Weiss reaction. However, superoxide reacts many times faster with nitric oxide (NO), than with ferric iron, leading to the formation of peroxynitrite (ONOO−), which is a potent oxidising and nitrating agent with properties and reactivity similar to hydroxyl radicals. Consequently ONOO− is a candidate for the initiation of oxidation reactions following brief ischaemia–reperfusion injury . The production of reactive nitrogen intermediates such as ONOO− is reflected in vivo by the formation of the amino acid derivative 3-nitrotyrosine. Recently, we have developed a sensitive method for the quantitative analysis of tissue nitrotyrosine which avoids the artefactual formation of nitrotyrosine that can occur with more conventional protein preparative steps.1 The present study sought to test the hypothesis that myocardial stunning causes increased formation of tissue nitrotyrosine. Large White pigs (mean (SD) weight 38 (4) kg) were anaesthetised and prepared as previously described2 to allow temporary occlusion of the circumflex coronary artery with simultaneous recording of haemodynamic parameters, circumflex coronary blood flow (group A only) and regional and distal myocardial contractile function by sonomicrometric segment shortening. Following 30 minutes of stabilisation, regional ischaemia–reperfusion was induced by 10 cycles …